Shares were dropped as much as 18 percent in premarket trading when the report was released.

The company issued weak guidance as well, with adjusted EBITDA between $215 million and $235 million. The full year projections declined compared to last quarter's estimates, with stock-based compensation expenses ranging from $300 million to $350 million as opposed to $350 million to $450 million projected last quarter. It also increased its capital expenditures rates for the year from $450 million and $500 million estimated last quarter to $375 million and $450 million.

For the last quarter, Twitter reported 336 million monthly active users. The platform blamed not moving to paid SMS carrier relationships in certain markets where users have better access to Twitter or Twitter Lite, making changes to improve the "health" of the platform and some impact from GDPR, a set of regulations in the European Union intended to protect consumer data. In total, Twitter estimates about 3 million accounts were affected by these three reasons.

Twitter removed about 70 million accounts in May and June, but Twitter chief financial officer Ned Segal said most of those were not included in its reported metrics because they were not active on the platform for 30 days or more.

The company also recently purged fake accounts, but those changes occurred after the close of the second quarter, so it didn't affect MAUs in this report. Twitter warned MAUs could go down even more next quarter.

"As a result of our health work, decisions not to renew or move to paid SMS carrier relationships in certain markets, and our decision to allocate resources towards GDPR and health, MAU could decline on a sequential basis in Q3," it said in its shareholder letter. "Based on our current level of visibility, we expect the decline to be mid-single-digit millions of MAU."